The synthesis of high temperature materials by exothermic reaction is well known in the art. This process offers the potential for cost reductions during material fabrication. In general, a problem with this process is that the reactant products are porous and have to be consolidated in a subsequent step. This compromises the advantages of the overall process. Several approaches have heretofore been devised for applying pressure either during or immediately following the exothermic reaction to promote densification in a single step. These approaches typically require expensive equipment such as a hot press; and, once again, the cost advantages of the exothermic synthesis approach are sacrificed.
Materials fabricated in accordance with this process have a wide range of applications in energy, aerospace, and defense systems. Components fabricated by this process, for instance, have improved physical properties and high strength-to-weight ratios. For instance, a dispersed phase composite, such as alumina (Al.sub.2 O.sub.3) reinforced with approximately 30 percent by weight of titanium carbide (TiC), exhibits good electrical conductivity, as well as high hardness, strength, and fracture toughness. This desirable combination of properties makes this type of composite useful, primarily for ceramic cutting tool applications. In spite of the obvious advantages of using these materials, however, their utilization has been limited by the difficulty and expense of fabrication. Additional and expensive equipment and processes are required to obtain materials with closed porosity.
Commercially available TiC-Al.sub.2 O.sub.3 composites are generally fabricated by hot pressing powder mixtures at temperatures above 1600.degree. C. Alternatively, a number of recent investigations have demonstrated that pressureless sintering at temperatures in excess of 1800.degree. C. can be used to attain closed porosity. After final densification by subsequent hot isostatic pressing, the properties are comparable to hot pressed materials. Although this procedure lends itself to near net shape forming, processing costs are still high due to the need for hot isostatic pressing.
Preparation of composites by exothermic reaction has been extensively investigated in the art. There has been limited success, however, in producing densified, useful materials. Additionally, there have been prior art efforts to combine exothermic synthesis with dynamic consolidation in a single process route. Although this approach has been partially successful, it has not heretofore achieved the results necessary for successful commercial fabrication of such materials.
The development of new, cost effective fabrication techniques for improved composite materials has been identified as a strong national need by several federal agencies including the Department Of Energy (DOE) (energy savings during fabrication and through use in transportation/conversion systems), NASA (advanced airframe development), Department Of Defense (DOD) (composite armor materials, advanced aircraft, weight reduction in defense systems), and Bureau Of Mines (BOM) (high temperature, wear-resistant materials).
In an effort to produce such composite materials, a new processing approach has been developed in accordance with the present invention. This approach combines the techniques of combustion synthesis and dynamic consolidation utilizing explosive-forming techniques to fabricate composites rapidly in a single processing operation. Composites such as TiC-Al.sub.2 O.sub.3 mixtures can be produced by exothermic reaction using low cost reactants. The expense of high cost starting powders is also eliminated. Additionally, since the cost of explosives and experimental assemblies is low compared to hot pressing or hot isostatic pressing facilities and because full densification is possible without any external heating source, the overall processing costs are relatively low.